Add IPC to query capabilities of video input devices.

content/common/media/media_devices.mojom

Index: content/common/media/media_devices.mojom
diff --git a/content/common/media/media_devices.mojom b/content/common/media/media_devices.mojom
index d53232e580266f2337d724cee50c8786666f33b9..2ef7a7f69795e528a20c846a2c2a61ead05896ae 100644
--- a/content/common/media/media_devices.mojom
+++ b/content/common/media/media_devices.mojom
@@ -4,6 +4,7 @@
 
 module mojom;
 
+import "media/capture/mojo/video_capture_types.mojom";
 import "url/mojo/origin.mojom";
 
 [Native]
@@ -12,6 +13,24 @@ enum MediaDeviceType;
 [Native]
 struct MediaDeviceInfo;
 
+// The values for this enum match the ones defined in
+// https://w3c.github.io/mediacapture-main/#def-constraint-facingMode
+// with the addition of UNKNOWN, which would map to the empty string in
+// JavaScript.
+enum FacingMode {
+  USER,
+  ENVIRONMENT,
+  LEFT,
+  RIGHT,
+  UNKNOWN

[hta - Chromium, 2017/01/27 10:40:47]

Is there a particular reason for not calling it NONE and putting it first? This
just seems like a departure from existing patterns.

[Guido Urdaneta, 2017/01/27 14:10:47]

Changed to NONE. Wasn't aware of the pattern.

+};
+
+struct VideoInputDeviceCapabilities {
+  string device_id;
+  array<media.mojom.VideoCaptureFormat> formats;
+  FacingMode facing_mode;
+};
+
 // This object lives in the browser and is responsible for processing device
 // enumeration requests and managing subscriptions for device-change
 // notifications.
@@ -24,6 +43,14 @@ interface MediaDevicesDispatcherHost {
                    bool request_audio_output,
                    url.mojom.Origin security_origin)
                        => (array<array<MediaDeviceInfo>> enumeration);
+  
+  // Returns a list of video devices and their capabilities.
+  // If there is a user-preferred device, it is the first in the result.
+  // The result of this function is intended for the implementation details
+  // of algorithms such as settings selection for getUserMedia.
+  // Do not expose the data contained in result of this function to JavaScript.
+  GetVideoInputCapabilities(url.mojom.Origin security_origin)
+      => (array<VideoInputDeviceCapabilities> video_input_device_capabilities);
 
   // Creates a subscription for device-change notifications for the calling
   // frame/security origin. It is the responsibility of the caller to send